As I am one of the current map designers here I can tell you, I think there is no perfect map everyone is looking for.
The main reasons I had starting the map design was the lack of 5 player maps. The time I have installed cncnet and began to play TD online was when the limit of players was already maxed out at 5, but most maps were designed for the previous cncnet version with the 6 player maximum.
That time no really good 5 player games came out, most of the time players went for 4 player matches. My first intentions were:
Space is limited to 62x62 which is small with the wrong map design, so I'd try to squeeze the most space out of it. The space of the 6th player is lost space which imbalances the whole map in a 5 player game (2 players will always have more room where no attacks may come from).
If you have the space to build big bases with 5 players you will need lots of resources if you like the longer battles (I personally like them more than the ultra short rush battles), otherwise the tiberium is gone after 3 minutes if every player has more than 4 refineries.
These ways of building maps granted longer fun for 5 players and everyone could build a big base, not limited by narrow passages that only allow like 2 refs, 1 airstrip and 1 radar.
The "turtle" players also went good with that kind of map design, since I think the campaign intends the player to rather turtle (why else do so many maps have pre built bases for player and computer that are surrounded with walls and turrets at the entrance in a rectangle shape).
I think that is why many beginners favor that style, they don't really know a different way to build and many players want to have their beautiful looking base (just like the computer's bases in the campaign).
The next steps in my map designing were to try to solve problems that came out of the last created maps such as: paths for infantry, pathwidth change for having a balance between open space and narrow passages (GDI VS NOD favor), harvester logic, balanced amount of tiberium, balanced space, balanced safety by environment, balanced starting points and so on....
So during the map creation it was rather a path of evolution and learning how the game works to finally find out that you can't favor each tactic, both sides, maybe just because of the game's logics (harvester NW logic, south advantage, west NOD disadvantage...).
In my last maps I tried to get as much knowledge into them, while at the same time making it natural, even, all-tactic-friendly and balanced as much as possible.
My conclusion after over 20 maps: you can't have it all, there is always one or more aspects your map will lack. Don't consider only the pro players, beginners also have their right for their view of the game.
Old style maps with less tiberium are good for 1 vs 1 games, in 5 player ffa games you wont have the same fun, the games will be over much faster, mainly because the tiberium grows too slow to let the game continue in action.
But my latest intention was not to build the perfect map (as some here tried to archieve just like the exact pentagon maps), it was to have a wider range of maps for every player's demands.